1. Field of the Invention
The present invention relates to a display device.
2. Discussion of the Background
Currently, as the demand for lighter and thinner monitors and TVs is increasing, cathode ray tubes (CRTs) are being replaced by liquid crystal displays (LCDs).
However, because the LCD is a passive display device, an additional back-light as a light source is needed, and the LCD has various problems such as a slow response time and a narrow viewing angle.
Among the flat panel displays, an organic light emitting device (organic light emitting diode display, OLED display) has recently been the most promising as a display device for solving these problems.
The organic light emitting device includes two electrodes and an organic light emitting layer interposed between the two electrodes. One of the two electrodes injects holes and the other injects electrons into the light emitting layer. The injected electrons and holes are combined to form excitons, and the excitons emit light as discharge energy.
Because the organic light emitting device is a self-emissive display device, an additional light source is not necessary such that the organic light emitting device has low power consumption, and it can be manufactured with a thin structure. Also, the organic light emitting device has a high response speed, a wide viewing angle, and a high contrast ratio, as well as a simplified manufacturing process compared with the liquid crystal display.
However, the organic light emitting device (OLED) may have an opaque and highly reflective electrode that is made of a highly reflective metal such as aluminum (Al) or silver (Ag) with a positive polarity or a negative polarity without regard to emitting direction. Accordingly, the metal functions as a mirror when the organic light emitting device is exposed to external light such that the contrast ratio is reduced.